1. Field of the Invention
The present invention relates to a marine backhoe dredge for excavation and mining applications under water. In particular, the present invention is directed to a sub-aqueous backhoe dredge which includes a counterbalancing system that increases the hoisting capacity and/or the hoisting speed of the backhoe.
2. Description of Related Art
A variety of hydraulic excavators, also called backhoe dredges, are known for hoisting hard in-situ and pretreated materials. A backhoe dredge typically includes a rotating frame and an attachment assembly consisting of a mono-block boom, stick and bucket. For example, U.S. Pat. No. 4,676,052 to Hawk discloses a self-propelled dredge which includes a two-piece boom and sealed bucket for removing silt, muck, and plant growth from the bottom of lakes, and ponds, whereas U.S. Pat. No. 3,086,305 to West discloses a dredge which includes a barge having a crane unit mounted thereon and spuds pivotably mounted to the barge.
Hydraulic excavators were originally used for land operations in which the excavated material was hoisted only through one medium, air. In contrast, marine backhoe dredges are required to hoist excavated material through two media, initially water, then air. Due to well-known principles of buoyancy, a backhoe has a greater hoisting capacity while submerged under water, than it does when hoisting loads in an air-medium. Due to this disparity in hoisting capabilities, problems often arise. Simply, the marine borne backhoe dredge often times hoists an excavated load in the water medium that actually exceeds its hoisting capacity in an air medium. In this regard, the backhoe is not sufficient for hoisting the excavated load when the backhoe emmerges from the water surface into the air medium.
Presently, when a backhoe with a greater hoisting capacity is needed to excavate or mine heavily compacted materials, a larger sized backhoe must be utilized in order to hoist the heavy material. One of the drawbacks of having to substitute the backhoe dredge with a larger sized backhoe is that current hydraulic technology cannot be further scaled to larger sized loads. In other words, current hydraulic technology dictates and limits the maximum size of a backhoe. Therefore, if the maximum sized backhoe dredge still lacks the capacity to hoist the load, little alternatives for excavating heavy loads exist.
Thus, there remains a need for an efficient and alternative apparatus that has an increased hoisting capacity and hoisting speed of the current backhoe dredges and is not limited by current hydraulic technology. The present invention now seeks to resolve these problems.